Slag screen for refining furnace

ABSTRACT

A slag screen is placed at the outlet of a refining furnace which includes a plurality of cooling tubes covered with insulation and attached at both ends to the furnace with means to control the passage of cooling fluid through the tubes and automatic temperature controlled valve to control the flow of cooling fluid through the tubes to obtain the desired temperature on the surface of the insulation to collect the optimum amount of slag and dust, to obtain the proper spacing for the passage of gases from the refining surface.

United States Patent [1 1 Ojima et al.

[111 3,746,324 1451 July 17,1973

[ SLAG SCREEN FOR REFINING FURNACE [75] Inventors: Masaki Ojima, Akashi; Masahiro Arata, Kobe, both of Japan [73] Assigncc: Kawasaki Jukogyo Kabushiki Keisha. Kobe, Japan [22] Filed: Sept. 8, 197] [21] App]. No.: 178,724

52 us. 01.; 266/1 R 51 Int. Cl. C2lc 5/46 58 Field Of Search 266/1 R, 34 R, 35, 266/13, 15-17, 31

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 1,142,888 1/1963 Germany 266/34 R Primary Examiner-Gerald A. Dost Attorney-Milf0rd A. .luten [57] ABSTRACT A slag screen is placed at the outlet of a refining fur nace which-includes a plurality of cooling tubes covered with insulation and attached at both ends to the furnace with means to control the passage of cooling fluid through the tubes and automatic temperature controlled valve to control the flow of cooling fluid through the tubes to obtain the desired temperature on the surface of the insulation to collect the optimum amount of slag and dust, to obtain the proper spacing for the passage of gases from the refining surface.

4 Claims, 2 Drawing Figures SLAG SCREEN FOR REFINING FURNACE This invention treats of improvement of the slagscreen in point of catching slag-ash by arranging it in a shop-curtain style at the outlet of the refining furnace or the combustion furnace of the boiler which generates hot gas containing a large amount of slag and ash.

The slag-screen placed at the outlet of the refining furnace and the combustion furnace should, of course, display the greatest possible catch effect of the slag and ash with a view to their removal, but thereby it must not excessively increase draft loss of gas flow, and in the case of the refining furnace, it is desirable to minimize the absorption of the internal heat by this slag-screen.

For this purpose, the well-known screens are so designed that the water cooling tube be adopted which circulates the cooling water from the inner tube to the outer tube and that, at the same time, the outer surface of the tube be covered with refractory material so as to reduce internal heat absorption, but there are quite many cases where the thickness of the refractory material previously determined in prospect of the heat load in the furnace does not meet the actual condition at the time of its operation, and ideal superficial temperature cannot be maintained; generally, the thickness of ash sticking to the screen varies with the fluctuation of the heat load of the furnace, and when the screens are fixed at regular pitches, the load drops and causes thesticking thickness of the slag on the screen to increase, thereby clogging the gas passage, or conversely, the load rises and causes the sticking thickness of the slag and ash to decrease, and the too wide-pitches of the screen deteriorate the catch effect. Such undesirable results are produced.

This invention is intended to remove the abovementioned defects by installing (1) the flow controller or (2) the temperature controller for the cooling medium at the inlet at the cooling medium supply circuit of the slag screen placed at the outlet of the refining furnace, and at the same time, (3) by installing the tem perature detector at the circuit discharging the cooling medium from the slag-screen, and by operating the above-mentioned controllers by means of this detector, thereby automatically controlling the external temperature of the screen even during the operation of the furnace.

The essential points of this invention are concretely explained as follows by reference to the drawings mentioned below:

HO. 1 is a cross-section of this invention as actually applied to the coppersmelting furnace.

FIG. 2 is a cross-section showing serially the structures of the principal parts of the well-known slag screen.

Explanations begin with FIG. 2: the well-known slag screen. The tubing that constitutes the screen is dualone inner tube IA and outer tube 2A. The cooling water supplied at one end of the inner tube is discharged l'rom its other end into the space between the inner and outer tubes. and then flows out from the end of the outer tube, thereby protecting its own material from high temperature. Also, it is so designed that, if necessary, the outer surface be covered with the refractory material 3A, thereby raising its surface tempera ture and reducing the heat absorption. but, as de scribed above, even if the thickness of the refractory material is previously designed in prospect of the heat load in the furnace, it often does not meet the actual condition at the time of operation, and an ideal surface temperature cannot be maintained, and when the heat load of the furnace fluctuates, the layer of ash sticking to the screen also tends to change its thickness, that is, if the load goes up, the slag decreases in thickness, and if the load drops, the slag increases in thickness, but if the screens are fixed at regular pitches, the load drops and the layer on the screen increases its thickness, thereby clogging the gas passage, or conversely, the load rises and the layer of the slag and ash gets thinner, and the excessively wide spaces of the screen pitches deteriorate the catch effect. Such undesirable results are brought about.

FIG. 1 shows an illustration of this plan as actually applied to the copper smelting furnace. 1 show the screen tubes installed at the outlet of the furnace F that keep inside the flow circuit for the cooling medium. 4 and 5 show the supply and discharge circuits of the cooling medium to and from the screen, respectively. 2 shows the temperature detector of the cooling medium at the outlet of the screen, and 3 shows the flow control valve.Tl and FC show'temperature indicator and flow controller respectively of the cooling medium.

This plan, as mentioned above, is intended to detect by means of the detector 2 the temperature of the cooling medium, such as air, hot water, superheated steam, Dowtherm, molten lead, and etc. before sending them to the screen 1, and to operate the control valve 3 according to the quantity thus detected, and to control the flow, thereby invariably maintaining the tube wall temperature of the slag-screen at a proper degree, and to invariably conduct the catching of slag and ash in a stabilized manner without cooling the interior of the furnace to excess, regardless of the amount of the heat load of the furnace.

This plan, which, as stated above, makes possible the control of the outer temperature of the screen even during the operation of the furnace, is effective in the performance of stabilizedoperations in that it eliminates all of the defects attendant upon the WGllrkl'lOWfl installations-that the temperature in the furnace is cooled to excess because of the installation of the screen at the outlet of the waste gas of the .fumace, or that the fluctuation of the heat load obstructs the gas flow or deteriorates the catch effcct,--and also in that it constantly yields satisfactory catch effects for slag and ash regardless of changes in their contents and melting point.

What we claim:

1. A slag screen for a refining furnace comprisng a tube, insulating material covering the tube means to cause cooling fluid to pass through the tube including an inlet and an outlet, a temperature indicator responsive to the temperature of the fluid through said outlet, a flow controller to control the flow of fluid passing through the tube to control the temperatrue of the tube whereby the exposed surface of the insulating material can be maintaned at an optimum temperature to collcct dust and slag issuing from said refining furnance while maintaining the proper thickness of the build up of slag and dust to permit the flow of waste gas from the furnace while catching the slag and dust.

2. The invention according to claim 1 in which an insulating material surrounds the tube.

3. The invention according to claim 1 in which the temperature control flow mechanism controls a valve in the inlet to the tube.

4. The invention according to claim 1 in which there are a plurality of tubes in spaced juxtaposition extending across the outlet of a refining furnace and the tubes are fixed to the refining furnace at both ends whereby all the gas and slag from the furnace must pass through the screen and the spacing between the accumulated dust and slag adhering to the screen can be accurately controlled for optimum operating conditions. a and dust to permit the flow of waste gas from the furnace while cataching the slag and dust.

2. The invention according to claim 1 in which an insulating material surrounds the tube.

contorlled for optimum operating conditions. 

1. A slag screen for a refining furnace comprisng a tube, insulating material covering the tube means to cause cooling fluid to pass through the tube including an inlet and an outlet, a temperature indicator responsive to the temperature of the fluid through said outlet, a flow controller to control the flow of fluid passing through the tube to control the temperatrue of the tube whereby the exposed surface of the insulating material can be maintaned at an optimum temperature to collect dust and slag issuing from said refining furnance while maintaining the proper thickness of the build up of slag and dust to permit the flow of waste gas from the furnace while catching the slag and dust.
 2. The invention according to claim 1 in which an insulating material surrounds the tube.
 2. The invention according to claim 1 in which an insulating material surrounds the tube.
 3. The invention according to calim 1 in which the temperature control flow meacnam controls a valve in the inlet to the tube.
 3. The invention according to claim 1 in which the temperature control flow mechanism controls a valve in the inlet to the tube.
 4. The invention according to claim 1 in which there are a plurality of tubes in spaced juxtaposition extending across the outlet of a refining furnace and the tubes are fixed to thE refining furnace at both ends whereby all the gas and slag from the furnace must pass through the screen and the spacing between the accumulated dust and slag adhering to the screen can be accurately controlled for optimum operating conditions. a and dust to permit the flow of waste gas from the furnace while cataching the slag and dust.
 4. The invention according to claim 1 in which ther are a plurality of tubes in spaced juxtaposition extending across the outlet of a refining furnace ad the tubes are fixed ot the refining furnace at both ends whereby all the gas and slag from the furnace must pass through the screen and the spacing between the accumulated dust and slag adhering to the screen can be accurately contorlled for optimum operating conditions. 